Page:Popular Science Monthly Volume 65.djvu/225

Rh Still, although the mutation experiments of de Vries have considerably strengthened the argument of Scott and other paleontologists, that slow, simultaneous mutation has also taken place among those fossil animals—the same experiments have, moreover, proved beyond any doubt that there is no such thing in nature as predetermined mutation in one special direction, but that, on the contrary, mutation occurs in very different and very divergent directions.

When once the mutation process leading to the formation of species has begun, the most different mutations, as we have seen above, arise. From our point of view, some of these may be called good, others bad or indifferent. About the permanence of any of them, it is, however, the surrounding conditions, acting by means of selection, that decide. And often the decision lies in another direction than would have been surmised from the human adjectives just named.

By the phenomenon of mutation the possibility exists that useless, and even to a certain extent prejudicial or noxious, specific characters may appear, a phenomenon which could never be reconciled with the views of Wallace.

For the greater part these characters are sure to be eliminated, but if other circumstances happen to be or to become favorable to a mutation, which was originally without any particular significance, it can then gradually develop and become adapted to certain modifications in the surrounding factors of life. The majority of the mutations, however, soon perish in the struggle for existence. Of those many elementary species that were doomed from the first, nothing has, of course, come down to us. in the archives of the fossil remains; only when their number has considerably increased in comparison with the parent species will it have been possible for them to survive, but then they have already risen to be a side branch, or may even be supplanting the parent stock.

The theory of mutation, as well as that which ascribes the origin of species to the selection of fluctuating varieties, enables us to understand how efficiency and adaptation in organic nature have come about by the mutual interaction of natural processes without the aid of supernatural intervention. The struggle for existence between species and mutations comes about in the same way as does the struggle for existence between individuals in the older view. Spencer's expression, however, 'the survival of the fittest,' must henceforth be interpreted as meaning 'the survival of the fittest species.' When we agree with de Vries that the gradual mutation of species is not necessarily the revelation of a foreordained design, this should be interpreted in the spirit of greater humility which befits the naturalist when he is confronted by the gigantic problems of organic nature. As long as a natural coordination of facts furnishes us with an intelligible causal